Decorative sheet material such as wall coverings are formed typically of paper, plastic, metal foil, or fabric material having a pattern or design printed or embossed on the front surface, with the other surface, or back, being coated by the consumer with a suitable adhesive, such as glue, cement, or the like (typically known as "wallpaper paste") by which the wall covering may be secured to a wall, ceiling or other surface. Other types of wall coverings include those having a plastic decorative surface and a backing of woven or non-woven fabric or paper. The backing or back surface is adapted to be coated by the user with the aforementioned adhesive in order to secure the wall covering to a surface. However, consumers dislike the inconvenience of mixing and applying the paste. Additionally, prepasted wall coverings need a water pan and this can be messy.
Generally, in conventional wall coverings, once the wall covering is applied to the surface, it may be shifted or adjusted thereon to a limited degree until the adhesive paste cures, or dries.
Pressure sensitive adhesives, hereinafter "PSA" or "PSAs" are known generally for their ability to provide adhesion between two substrates upon contact. PSAs rely on high initial tack and/or quick set-up reaction, or cure time for prompt or instant adhesion. However, PSAs with sufficiently high tack to hold a wall covering in place are very difficult to apply to a wall and then reposition, as occurs for example, while matching up patterns from one wallpaper strip to the next. Although suitable pressure sensitive adhesives have in the past been applied to wall coverings, attempts to reposition those same wall coverings generally have not met with success. Typically, wall coverings having PSA have fallen from the walls to which they were applied shortly after such application due to poor permanent adhesion; the wall covering cannot be slid and repositioned while in contact with the wall due to adhesive tack; the outline of various spacer means used to separate the adhesive from the wall in attempting to introduce some slip until a permanent adhesion is attained show through the decorative face of the wall covering; spacer means are often on the surface or embedded in the PSA so that upon development of slight adhesive contact with the wall, the spacers loose their effectiveness; manufacturing difficulties are encountered in placing the correct thickness or otherwise positioning of spacers or projections over an adhesive coating; and have other shortcomings.
The following references are illustrative of the prior art.
U.S. Pat. No. 3,301,741 Henrickson et al. of Jan. 31, 1967. Discloses a self-adhering wall covering comprising: a substrate such as paper; a pressure sensitive adhesive; and a separation means secured to or a part of the backside of the substrate. The spacer means are of a uniformly pebbly contour of raised adhesive protrusions on the back separated by intervening adhesive planar areas wherein the tips of the protrusions are of a friable non-adhesive material which crumble into particles upon the application of pressure to the substrate. Also, the tips of the adhesive projections can be coated with a non-adhesive coating.
U.S. Pat. No. 3,314,838 to Erwin of Apr. 18, 1967. Discloses PSA mixed with microspheres which on drying on the back of a wall covering leaves a thin film of adhesive over the microspheres. Allegedly, the adhesive does not interfere with repositioning until force is applied to break the spheres and permit more adhesive contact.
U.S. Pat. No. 3,331,729 to Danielson et al. of Jul. 18, 1967. Discloses wall coverings which are allegedly repositionable and slidable due to micro balloons over or imbedded in the PSA.
U.S. Pat. No. 3,554,835 to Morgan of Jan. 12, 1971. Shows an allegedly slidable PSA film. When force is exerted on the face of the film, PSA on its backside extrudes from below dots of release material and adheres to the receptive surface, or the dots may be fractured or sink into the PSA.
U.S. Pat. No. 3,663,269 to Fischer et al of May 16, 1972. Discloses a wall covering having a coating of dry encapsulated adhesive on its back surface which is made tacky by the application of heat and/or pressure.
U.S. Pat. No. 3,857,731 to Merrill et al. of Dec. 31, 1974. Discloses a reusable, rebondable sheet having PSA with microspheres embedded in a binder.
U.S. Pat. No. 4,054,697 to Reed et al. of Oct. 18, 1977. Discloses a wall covering having PSA on its back side. The PSA has a coating of resilient non-adhesive particles thereon or imbedded therein.
U.S. Pat. No. 4,376,151 to Parrotta of Mar. 8, 1983. Discloses business forms having PSA on their back side and superimposed thereover is a layer of microspheres which are displaced by application of pressure.
U.S. Pat. No. 4,556,575 to Ochi of Dec. 3, 1985. Discloses a relocatable, multiple use adhesive sheet wherein the back is entirely covered with PSA in which elastic microspheres are embedded.
U.S. Pat. No. 4,735,837 to Miyasaka et al. of Apr. 5, 1988. Discloses self-adhesive wall covering comprising: a substrate; PSA; and elastic micro-balls embedded in the adhesive.
U.S. Pat. No. 5,080,957 to Leseman et al. of Jan. 14, 1992. Discloses a reinforced tape having ribs on one side thereof wherein a PSA is applied over either the front or back side of the tape.
U.S. Pat. No. 5,108,811 to Shippen of Apr. 28, 1992. Discloses a removable, reusable window insulation comprising a thermal insulating material such as polyethylene foam coated with PSA.
U.S. Pat. No. 5,141,790 to Calhoun et al. of Aug. 25, 1992. Discloses a repositionable PSA sheet wherein the PSA has clumps thereon with non-adherent material distributed on the clumps.
JP 61-115981 to Chugokee of Jun. 3, 1986. Discloses a PSA sheet consisting of a base sheet having hollow protrusions which are filled with PSA.
EPO 0367651 to O/Y KYRO A/B of May 9, 1990. Discloses strippable wallpaper having on its glueable surface, areas of water activated adhesive applied over hydrophobic release agent or areas of such release agent applied over such adhesive for easy release from a wall.
PTC WO 91/09725 of Jul. 11, 1991. Discloses a carpet cushion having PSA coated thereon and a scrim webbing or other spacer element laid on or into the PSA after the adhesive has been applied.
Our invention provides a decorative sheet such as a wall covering that is manufactured with an adhesive on its back or working surface, thus resulting in a so-called self-adhesive or PSA wall covering that may be applied to a support surface and yet repositioned, and which does not require the use of additional cement, glue or wallpaper paste. This invention also provides a decorative sheet which can make adhesive contact on slight initial pressure, yet which can be repositioned before and until a final desired position is achieved.
A substantial area of the decorative sheet working surface is provided with a tacky, pressure sensitive adhesive. However, remaining on the working surface area are spaces which are not covered by adhesive which provide uniformly distributed discontinuities or spaces. Uniformly distributed non-adhesive projections which have a height equal to or greater than the thickness of the adhesive are provided within the discontinuities on the back side and out of contact with the adhesive.